To ensure fuel feed to the main engine, heavy fuel oil (HFO) is separated though first being pumped into a settling (buffer) tank. The following service tank or day tank, which is filled via a continuous overflow from the settling tank, directly supplies fuel into the main engine. Heating coils in both of these tanks maintain an even temperature between +75° C and +90° C. A reliable level measurement in these tanks guarantees continuous manoeuvrability of the ships.